Selenium: Health Benefits and Risks of Overdose
Selenium is an essential micronutrient best known for its antioxidant properties. It is part of 25 selenoproteins that play many different roles in the body, ranging from promoting hormone production and strengthening the immune system to possibly protecting against cancer. Selenium is found naturally in many foods and water. Its amount in the food largely depends on the concentration of selenium in the soil, in which the plants used for human consumption or to feed animals were grown.
Dietary selenium occurs in two forms – as inorganic compounds (found in water) and organic compounds (meat, plants). Both forms can be absorbed in the body. Most people in the US get adequate amounts of selenium from their diet. However, in the UK, parts of Europe and China the soil is poor in selenium and dietary intakes are low. In these regions, animal foods can provide more selenium than plant foods.
Recommended Intake Levels of Selenium
Recommended dietary allowances (RDAs) and tolerable upper intake levels of selenium expressed in micrograms per day (not milligrams) are as follows:
|Age (both genders)||RDA (mcg)||Upper Limit (mcg)|
|Birth to 6 months||15||45|
|7 – 12 months||20||60|
|1 – 3 years||20||90|
|4 – 8 years||30||150|
|9 – 13 years||40||280|
|14 years and older||55||400|
Potential Health Benefits of Selenium
Being an essential part of some 25 proteins, selenium has many important roles in the body. It protects cells from oxidative damage, enhances immune system function, regulates thyroid metabolism, aids in the production of several key hormones (including prostaglandins), prevents platelets from aggregating, plays a critical role in reproduction and thus helps ensure fertility, cardiovascular health and helps protect the body from infections and possibly also from cancer. In addition, selenium may help reduce inflammation associated with rheumatoid arthritis. Scientists are examining the potential of selenium for the treatment of a number of diseases including asthma, age-related decline in brain function, dandruff, thyroid disease and prostate cancer.
Selenium Deficiency and Symptoms
Selenium deficiency is rare in the US and Canada but appears to be more common in the UK, parts of Europe and in New Zealand, especially among vegetarians and vegans. Patients undergoing kidney dialysis, those with HIV or chronic digestive ailments hindering an adequate absorption of nutrients from food may also be deficient in selenium. However, eating a handful of Brazil nuts a day or taking supplements may provide the missing selenium.
A lack of selenium may lead to Keshan disease, heart disease, male infertility, osteoarthritis, birth defects and cataracts. Symptoms of selenium deficiency include hair loss, skin and nail discoloration and nail brittleness, weak immunity, fatigue, muscle weakness, fertility problems, difficulty concentrating, hypothyroidism, heart problems and metabolic disorders.
Health Risks of Taking Selenium and Symptoms of Overdose
Selenium may interact with some medications including certain antacids, birth-control pills, cholesterol-lowering agents, corticosteroids and chemotherapy drugs. In addition, selenium may interfere with beneficial effects of certain nutrients such as niacin and iodide.
Although selenium is more effective as an antioxidant in the presence of vitamin E, one recent study has found that men who take selenium supplements in conjunction with vitamin E supplements may increase their risk of prostate cancer. These findings contradict earlier observations of cancer protective effects of these two nutrients.
Selenium overdose is rare and usually occurs as a result of excessive supplementation. Paradoxically, too much selenium may cause symptoms similar to those of deficiency such as hair loss, discoloration of skin and nails, tiredness, irritability and nervous disorders. Other symptoms of selenium toxicity include nausea, vomiting, diarrhea, metallic taste in the mouth, halitosis (bad breath), facial flushing and skin rash. Severe overdose can lead to kidney and cardiac failure and, in extreme cases, even to death.
Dietary Sources of Selenium
Natural forms of selenium can be found in Brazil nuts, seafood, meats, especially organs meats, poultry, eggs, grains and cereals, spinach and dairy products. Multimineral supplements containing selenium and stand-alone supplements are available but should only be taken if recommended by a physician.